The increasing influx of migrant workers has helped push this metropolis' population by almost 11 percent to nearly 18 million since 2000, said a statistic report released this week.

The population rise includes new immigrants to the city and new arrivals at its maternity wards.

The comparatively higher birth rates among migrant families in 2005 gave the city its first positive birth-death ratio since 1993, said the report of the municipal statistics bureau, part of a nationwide population survey.

Shanghai's residential population rose to 17.78 million in 2005, comprising 13.4 million people with residency permits and 4.38 million migrants who lived in the city for more than six months, the report said.

The population increased by 1.7 million since 2000, and more than 80 percent of the newcomers were migrants, it said.

"Migrant workers have become an indispensable part of the city's economy by doing things local residents are not willing to do," Hu Suyun, a researcher of the Shanghai Academy of Social Sciences, was quoted as saying by Shanghai Daily.

The immigrants often take jobs as construction workers, maids, waiters, waitresses and vegetable dealers, the newspaper said.

The survey indicated they also tend to have more babies than the typical long-term Shanghai resident.

The increasing number of migrant people has changed the city's population structure, the statistic report said.

Experts worry, however, that the soaring population may deplete the city's resources and exhaust its environment.

The survey also pointed up the continuing challenge brought by the city's aging population, the result of a baby boom in the 1950s. People age 60 or older accounted for 19.6 percent of the city's population last year compared with 18.3 percent in 2000.

"Shanghai will be 10 years ahead of the rest of China in terms of its aging society," the statistics bureau predicted.